In recent years, transparent organic polymer materials are used as transparent materials that replace inorganic glass. When these materials are used in optical resins, generally, the materials are required to have characteristics that are generally requested, for example, transparency, thermal properties and mechanical properties, and to have high refractive indices.
One of the technologies relating to such a resin is described in Patent Document 1. In the same document, a metal-containing thietane compound is described. Furthermore, a high-refractive index optical resin having a refractive index (nd) exceeding 1.7 is described. Patent Document 3 describes a method for producing a resin using a lanthanoid-containing thiol.    [Patent Document 1] WO 2005/095490    [Patent Document 2] Japanese Laid-open patent publication No. 2003-327583    [Patent Document 3] Japanese Laid-open patent publication No. 61-166804